This invention relates to a coil bobbin and an objective lens drive device, and particularly to a coil bobbin having a plurality of coils and to an objective lens drive device in which this coil bobbin is used.
Optical recording medium, for example optical disc recording and/or reproducing apparatuses perform recording or reproduction of information signals on an optical recording medium by irradiating a light beam from an optical pickup onto the recording medium. The light beam emitted by the optical pickup is focussed onto the recording surface of the optical recording medium by an objective lens. The objective lens is so driven in a focussing direction and a tracking direction by an objective lens drive device that it follows-up any eccentricity and vertical motion of the optical disc. An electromagnetic-drive actuator is used as this objective lens drive device.
An objective lens drive device is constructed for example as shown in FIG. 1. In FIG. 1, an objective lens drive device 1 has a lens holder 2, a coil bobbin 3, a fixed portion 4, a plurality of supporting members 5, a yoke 6, a permanent magnet 7 and a base 8.
An objective lens 2a is mounted in one end of the lens holder 2, and the coil bobbin 3 is mounted in the other end. The lens holder 2 is supported by the plurality of supporting members 5 movably in a direction parallel to the optical axis of the objective lens 2a, namely the focussing direction Fcs, and in a horizontal direction orthogonal to the optical axis of the objective lens 2a, namely the tracking direction Trk.
The coil bobbin 3 is formed in a square-shaped having a central through hole and is so fixed in the lens holder 2 that the through hole extends in a direction parallel to the optical axis of the objective lens 2a. The coil bobbin 3 has a focussing coil (not shown in the drawing) wound thereon along the direction of the optical axis of the objective lens 2a and a plurality of tracking coils (not shown in the drawing) are arranged on one side thereof. The tracking coils are composed of lead wires wound in rectangular planar coils. The focussing coil and the tracking coils are connected to electricity supply wires (not shown in the drawing), and a focussing drive signal and a tracking drive signal are supplied to the respective coils through these electricity supply wires. The plurality of supporting members 5 are made of elastic members such as plated springs.
The plurality of supporting members 5 each have one end fixed to the lens holder 2 and the other end fixed to the fixed portion 4 so that they are mutually parallel. As a result, the plurality of supporting members 5 support the lens holder 2 movably in the focussing direction Fcs and the tracking direction Trk. The fixed portion 4 is mounted on the base 8.
The yoke 6 has mutually opposing yoke portions 6a and 6b and is formed in a cross-sectionally U-shaped. A permanent magnet 7 is mounted on one of the yoke portions 6a, 6b. In the construction shown in FIG. 1, the permanent magnet 7 is mounted on the yoke portion 6a and inserted into the through hole of the coil bobbin 3, and the other yoke portion 6b faces the focussing coil and the tracking coils of the coil bobbin 3. The base 8 is formed in a platelike shape and is made of a metallic material, and is provided the yoke 6 on a portion thereof.
In the objective lens drive device 1 constructed as described above, a focussing drive signal and a tracking drive signal are supplied to the focussing coil and the tracking coils through the electricity supply wires (not shown). Because as shown in FIG. 1 the focussing coil and the tracking coils are located in a gap between the yoke portion 6b and the magnet 7, the magnetic fields generated from the focussing coil and the tracking coils cross the magnetic flux between the magnet 7 and the yoke portion 6b. As a result, driving forces which move the lens holder 2 in the focussing direction Fcs and the tracking direction Trk are generated, and the lens holder 2 is moved in the focussing direction Fcs and the tracking direction Trk in accordance with the focussing drive signal and the tracking drive signal. The light beam focussed onto the recording surface of the optical disc by the objective lens 2a is so controlled that it follows-up any eccentricity of the optical disc and any vertical motion of the recording surface of the optical disc.
In the objective lens drive device 1 shown in FIG. 1, the end portions of the lead wires of the focussing coil and the tracking coils are severally electrically connected by soldering or the like to terminal portions, not shown, provided on the lens holder 2. However, because the coil bobbin 3, the focussing coil and the tracking coils are small, and because the lead wires constituting the focussing coil and the tracking coil are thin, the assembly of connecting the end portions of the lead wires to the lens holder 2 has been complicated and difficult. Also, there have been such problems as that this kind of construction is not suited to machine assembly and cost savings cannot be achieved.
Furthermore, after the objective lens drive device 1 is assembled, continuity checking of the coils and measurement of the magnetic fields generated by the coils are carried out by voltages being impressed across the coil terminals, but in practice it has been difficult to perform coil continuity checking and measurement of the magnetic fields generated by the coils during the assembly process.